U.S. patent application number 13/442380 was filed with the patent office on 2012-11-15 for system and method for depositing material on a piezoelectric array.
Invention is credited to Deda Mampuya Diatezua, Rainer Schmitt, Roland Williams.
Application Number | 20120288641 13/442380 |
Document ID | / |
Family ID | 46969586 |
Filed Date | 2012-11-15 |
United States Patent
Application |
20120288641 |
Kind Code |
A1 |
Diatezua; Deda Mampuya ; et
al. |
November 15, 2012 |
SYSTEM AND METHOD FOR DEPOSITING MATERIAL ON A PIEZOELECTRIC
ARRAY
Abstract
A system having a print head for depositing material on a
piezoelectric array, where the print head and array are moveable
with respect to each other, and a computer for controlling movement
of the print head and array with respect to each other to locations
along the array, and controlling the print head to dispense the
material onto the array at such locations. The print head deposits
a pre-determined amount of material in one of dots, or in a line
with movement of the print head and array with respect to each
other. The system enables deposit of conductive material for
electrical connections to array elements. Non-conductive polymer
material may be deposited on the array before depositing conductive
material to create barriers avoiding unintended connection of array
elements by the conductive material. The system may also be used
for fabricating a piezoelectric array by depositing electro-ceramic
material.
Inventors: |
Diatezua; Deda Mampuya;
(WELLINGTON, FL) ; Schmitt; Rainer; (PALM BEACH
GARDENS, FL) ; Williams; Roland; (MARTINEZ,
CA) |
Family ID: |
46969586 |
Appl. No.: |
13/442380 |
Filed: |
April 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61516839 |
Apr 8, 2011 |
|
|
|
Current U.S.
Class: |
427/555 ;
118/696; 427/100 |
Current CPC
Class: |
H01L 41/37 20130101;
H01L 41/29 20130101; H01L 41/183 20130101 |
Class at
Publication: |
427/555 ;
118/696; 427/100 |
International
Class: |
H01L 41/24 20060101
H01L041/24; B05D 3/06 20060101 B05D003/06; B05D 5/12 20060101
B05D005/12 |
Claims
1. A system for depositing material on a piezoelectric array of
elements composed of electro-ceramic composite material comprising:
a print head for depositing a material on the array; means for
moving said print head and the array with respect to each other;
and a computer system for controlling said means to move said print
head and the array with respect to each other to locations along
the array, and controlling said print head to dispense said
material onto the array at the locations.
2. The system according to claim 1 wherein said material is one of
a conductive fluid or a non-conductive fluid.
3. The system according to claim 1 wherein said material is
conductive ink and said print head deposition at said locations
provides traces along the array in a first layer.
4. The system according to claim 3 wherein said print head
deposition at said locations further provide contact points upon
each of the elements of the array in a second layer in connection
to traces of said first layer.
5. The system according to claim 1 wherein said material is a
conductive material and said print head deposits conductive
elements along the array to provide connections at said locations
along said array.
6. The system according to claim 1 wherein said material is
non-conductive material and said print head deposits said material
at said locations between adjacent ones of said array elements.
7. The system according to claim 1 wherein said material has
viscosity enabling dispensing via said print head.
8. The system according to claim 1 wherein said system has first
and second modes, and in said first mode said material is
non-conductive material and said print head deposits said material
at a first plurality of said locations represent locations between
adjacent different ones of said array elements, and then in said
second mode said material is a conductive material and said print
head deposits conductive elements along the array in one or more of
traces or drops to provide connections at a second plurality of
said locations representing locations along different ones of said
elements of said array, in which said non-conductive material
deposited prevents unintended connection of deposited conductive
material to one or more of said elements of said array.
9. The system according to claim 1 wherein said print head is an
ink jet print head.
10. The system according to claim 1 wherein said array has filler
material between elements of said array binding said elements of
said array.
11. The system according to claim 1 wherein said array is utilized
as part of a finger print sensor.
12. The system according to claim 1 further comprising means for
facilitating sintering of said material deposited.
13. The system according to claim 1 further comprising means for
optically aligning said print head with the elements of said
array.
14. A method for depositing material on an array of elements
composed of electro-ceramic composite material and binding material
between said elements, said method comprising the step of: printing
conductive material along the array to provide conductor elements
to different ones of said elements of the array.
15. The method according to claim 14 further comprising the step of
printing non-conductive material onto said array prior to said
printing conductive material step at locations along the array
which prevents unintended connection of said conductive material
when said printing conductive material step is carried out.
16. The method according to claim 14 wherein said printing in by an
ink jet printer.
17. The method according to claim 14 wherein said printing step is
carried out in one or more layers upon the array.
18. The method according to claim 14 wherein said printing step is
carrying out by a print head movable along said array, and said
method further comprises the step of: optically aligning said print
head to one or more of said array elements prior to carrying out
said printing step along said one or more of said array
elements.
19. The method according to claim 14 wherein said printing step is
carried in one or more of traces along the array and connection
points to individual elements of the array.
20. A method for fabricating an electro-ceramic array comprising
the steps of: printing electro-ceramic material in dots upon a
substrate at array locations to a height greater than a target
thickness to provide elements of said array; sintering each of the
elements of said array; applying filler material between and over
the elements formed by the printing step; and grinding the array
along the top thereof until the target array thickness upon the
substrate is reached.
21. The method according to claim 20 further comprising the step of
printing conductive material along the array to provide connections
along different ones of said elements of said array.
22. The method according to claim 20 further comprising the step of
printing non-conductive material between adjacent ones of said
array elements.
23. The method according to claim 22 further comprising the step of
printing conductive material along the array to provide connections
along different ones of said elements of said array in which said
non-conductive material deposited prevents unintended connection of
deposited conductive material to one or more of said elements of
said array.
24. The method according to claim 20 wherein said sintering step is
providing by applying a laser to each of the elements of said
array.
Description
[0001] This application claims the benefit of priority to U.S.
Provisional Patent Application No. 61/516,839, filed Apr. 8, 2011,
which is herein incorporate by reference.
FIELD OF THE INVENTION
[0002] This present invention relates to a system and method for
the depositing material on a piezoelectric array, and particularly
to, a system for depositing material by a print head along a
piezoelectric array of elements of electro-ceramic composite
material of a 1-3 type or higher order. The system is useful for
depositing conductive material for making desired electrical
connections to array elements in one or more layers. The system may
also deposit non-conductive polymer material on the array before
depositing conductive material if needed to create barriers that
avoid unintended connections of array elements by the conductive
material when deposited. The system may also be used for
fabricating a piezoelectric array by depositing electro-ceramic
material to build-up array elements. The invention avoids thin
metal film deposition based photo-lithography process as commonly
used in the manufacture of semiconductors, which has been found
difficult in the manufacture of electro-ceramic composite materials
in dense arrays for piezoelectric fingerprint sensors. This
inventions described herein represent improvements in manufacturing
biometric sensing devices as described in U.S. Pat. No. 7,489,066,
which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] The miniaturization of electronic components and
increasingly dense levels of integration have resulted in the
evolution of processes to deposit electrical conductors used to
interconnect individual elements. The greatest progress has, of
course, been made in the semiconductor industry where lithographic
processes are used to define the pathways for the conductors and
the conductors themselves can be deposited in any of a number of
ways. For example, a metal conductor may be deposited using a
sputtering process wherein a plasma is created in an inert,
low-pressure gas environment and metal atoms released from a pure
metal target, being one of two electrodes sustaining the plasma,
are able to condense on the intended point of deposition, usually a
substrate. Another method common in the semiconductor world is to
bombard the recipient semiconductor wafer with ions to alter the
conductivity of the semiconductor itself. Many kinds of material
may be deposited using these kinds of techniques including
insulator and semiconductor materials.
[0004] When the recipient of the material to be deposited is a
flat, crystalline or amorphous substrate, an exemplar process would
be a photo-lithographic process and is considered to be relatively
straightforward. In this example, the substrate is first coated
with a suitable photo-resist of which many types are commercially
available. A photographic mask will have been prepared which mask
will define the intended layout of the pattern of the material
which is to be deposited on the substrate. The photo-mask will be
at the actual scale of the geometry of the intended part. The
photo-resist is normally applied to the substrate and dried, often
by baking. Considerable pains must be taken to assure an even
coating of consistent thickness to ensure even exposure. The
photographic mask is then placed over the resist-coated substrate
and the pattern exposed using a high energy light source, often
ultra-violet. The short wavelength of the light is beneficial in
that it allows good edge definition for the exposed pattern. The
photo-resist is developed and the unwanted resist is stripped away
and then the prepared substrate may be placed in the deposition
machine. The metal atoms will be deposited over the entire
substrate but when the resist covered areas are finally removed,
this leaves a conductor pattern on the substrate joining the
required elements together electrically.
[0005] When the substrate exhibits a high degree of flatness, the
process can be engineered to work reliably and repeatably but, when
surface flatness is uncertain then the quality of the deposited
material may vary to the point that it is no longer a
straightforward process. Uncertain variability in flatness
generally leads to poor repeatability and compromised process
yield. Steps in the height of the substrate material present
significant problems; edges tend to exhibit poor coverage by the
conductor and may prove to be points of failure when the item is
stressed over temperature and current.
[0006] Composite materials, such as of lead zirconate titanate
(PZT) material, present a particularly challenging difficulty. The
different constituents of the composite material exhibit differing
properties and a major hurdle to be overcome is change due to
temperature variation. In particular when the composite is of a 1-3
type or higher order, then the material is defined as being
continuous in one direction and the effects of temperature are
severe. When a metal is applied to the surfaces, there can now be
three different materials each with its own temperature
sensitivities which further complicates the problem with the
allowable temperature range for the part.
[0007] Moreover, the manufacturing process for certain composites
involves very high temperatures during the formation or sintering
of the piezoelectric material. Without very carefully controlled
cooling from such high temperatures, distortion is a significant
problem which can be difficult or even impossible to correct in any
subsequent step. This introduces dimensional variability into the
final composite structure that limits the use of photo-lithographic
semiconductor technologies because the substrate often exceeds
allowable limits such as the spacing consistency between elements
or flatness. A photographic process, being of fixed dimensions, may
be difficult to apply reliably with consequential yield
constraints. The use of a polymer in the composite further limits
the subsequent allowable process temperature, and it is apparent
that alternate technologies would be desirable to overcome these
difficulties.
[0008] U.S. Pat. No. 7,489,066 describes a biometric sensing device
of an array of discrete piezo electro-ceramic elements and filler
there between. The array of discrete electro-ceramic elements is
responsive to acoustic characteristics of parts of the finger.
Conductors are provided along the array enable signals to be
received from individual sensing elements which are processed to
provide a fingerprint image. During manufacturing of the device
such conductors may be applied by thin metal film deposition based
photo-lithography which has been found to have the above-described
problems due variability in array elements dimension and/or the
flatness of the surface of the arrays when conductors are applied.
Moreover, the photo-lithographic process may be unusable if the
piezo electro-ceramic array is large, such as 55 mm.times.55 mm or
larger.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
improve manufacturing of piezoelectric sensor arrays by providing a
system and method for depositing conductors onto electro-ceramic
composite arrays by printing, e.g., by an ink-jet printer or print
head, of conductive material(s) onto electro-ceramic composite
array to provide such conductors, thereby avoiding the drawbacks of
photo-lithographic deposition of conductors.
[0010] A further object of the present invention is to first apply
non-conductive material, such as a polymer, prior to depositing
conductive material in order to create barriers avoiding unintended
connection of array elements by the conductive material when
deposited.
[0011] It is another object of the present invention to fabricate
an electro-ceramic composite array by printing electro-ceramic
composite material at array locations in forming array elements of
desired height.
[0012] Briefly described the invention embodies a system having a
print head, such as ink-jet type print head, for depositing a
material on a piezoelectric array of elements composed of
electro-ceramic composite material, a mechanism for moving the
print head and the array with respect to each other, and a computer
for controlling the mechanism to move the print head and the array
with respect to each other to locations along the array, and
controlling the print head to dispense the material onto the array
at such locations.
[0013] The print head when actuated deposits a pre-determined
amount of material responsive to signals from the computer in one
of dots (drops), or along traces or lines in accordance with
movement of the print head and the array with respect to each
other. Preferably, the print head is movable by the mechanism in
multiple dimensions over the array which is disposed stationary on
a surface, plate, or substrate. The material deposited by the
system may be a conductive fluid, such as conductive metallic ink,
or non-conductive fluid, such as a liquid polymer. The array
represents a matrix of pillar-like structures of electro-ceramic
material of desired size, height, and density of distribution, with
a flexible filler material, e.g., epoxy, binding the structures
together, and a generally flat surface provided along the surfaces
of the pillar-like structures and the flexible filler material
there over which the print head may be selectively located.
[0014] When the material being deposited is a conductive fluid, the
system enables the print head to deposit the material directly onto
the composite array so as to make the electrical connections to the
individual elements of the array. Thus conductive elements or
conductors may be deposited by the print head on the array under
control of the computer, rather than by metal film deposition based
photo-lithography process. The material applied conforms to the
surface of the composite material of the array. Preferably, the
conductive elements are deposited in a first layer of locations in
traces or lines (generally parallel to each other) along the
surface of the array over array element(s) and filler material
between array elements, and then in a second layer of locations of
array elements in drop(s) to provide enlarged areas for contact
points. Thus, one or more layers of the conductive material may be
provided at such locations, where each layer of material at
locations is provided in a separated pass or path of the print head
over the array. The viscosity of the conductive fluid enables the
desired conductor line width or contact point size to be provided
by the print head when actuated by the computer system.
[0015] Different materials may be deposited by the print head at
different times. For example, the system may be operated in first
and second modes. In the first mode, the print head deposits
non-conductive material, such as a polymer, at a first plurality of
locations representing locations between adjacent different ones of
array elements to provide a polymer layer. After the polymer fluid
polymerizes, the system then operates in the second mode to provide
conductive material in one or more layers in which the print head
deposits conductive material, such as conductive ink, along the
array in one or more of traces or drops to provide connections at a
second plurality of locations representing locations along
different ones of the elements of the array. The non-conductive
material when deposited creates separators or barriers to avoid
unintended or unwanted connection of array elements by conductive
material by flow or wicking.
[0016] The present invention also provides a method for the
depositing material using a print head on a piezoelectric array of
elements composed of electro-ceramic composite material by
selectively printing conductive material along the array to provide
connections along different ones of the elements of the array. The
method may further provide for printing non-conductive material
between adjacent ones of the array elements prior to printing with
conductive material. The non-conductive material deposited prevents
connection of deposited conductive material to one or more of the
elements of the array when the printing conductive material step is
carried out.
[0017] The printing, such as by ink-jet printer, of the present
system and method solves the problem of forming conductors along
arrays by thin metal film deposition based photo-lithography
process, described earlier, which is difficult to reliably provide
conductor elements due to variability in array elements dimensions
and/or the flatness of the surface of the arrays when conductors
are applied among elements in the same array, and/or among
different arrays.
[0018] In applying conductor elements for an array for use in a
finger print sensing device, the system operates separately with
respect to top and bottom of the same array to deposit conductor
elements along the top and bottom array surfaces, respectively. The
system may operate upon one or multiples arrays at one time.
[0019] The system of the present invention may be used as part of
the fabrication method of an electro-ceramic composite array
itself. Such method provides printing electro-ceramic composite
material in dots or drops upon a substrate at array locations to a
height greater than a target thickness of the array to provide
elements of the array, sintering each of the elements of the array
(such as by a laser), applying filler material between and over the
elements, and grinding the array along the top thereof down until
the target array thickness upon the substrate is reached.
Thereafter, the completed array may have conductive material (or
non-conductive material and then conductive material) applied by
the system onto the array as described above.
[0020] In summary, the system of the present invention relates
generally to the deposition of materials on the surfaces of an
electro-ceramic array prepared as a 1-3 composite. Typically, a
multi-element transducer for pressure waves such as sound or
ultrasound, or indeed any transducer assembly that couples
mechanical motion and an applied or derived electric potential,
involves making more than one electrical connection to each of the
elements. In an array of elements, one connection may be shared
between some or all elements, for example, a common ground
connection.
[0021] Dense arrays of piezoelectric sensors may be fabricated by
creating a matrix of individual sensors. Such arrays may be used
for scanning, for example, surface features which may be in contact
with the array; one class of application of this type would be the
contact sensing of fingerprints or other skin features. In one
example, a matrix of electro-ceramic elements are bound in a
polymer structure, e.g., epoxy, so that the active elements are all
aligned but separated and spaced regularly throughout the polymer.
The array may be prepared as a single row or as a field of sensors
as described in the above incorporated U.S. Pat. No. 7,489,066. The
array elements may be connected by conductors located on the top
and bottom of the matrix so that each element is individually
addressable and so that each element may be activated independently
of its neighbors in the array.
[0022] Conductive elements such as conductive ink or fluid, may be
printed directly onto the composite array so as to make the
connections to the individual sensors. The conductive ink or fluid
may be sintered or cured after application. The viscosity of the
ink is such as to provide the desired thin width or dot size and to
minimize undesirable flow or wicking. The conductor may be the
result of the application of more than one layer of the conductive
ink or fluid. The ink or fluid may be selected so as to conform
well to the surface of the composite material. The requirement for
flatness of the array which is normally dictated by the
photo-lithographic process may be relaxed because the need for
intimate contact between a mask and a coating layer is removed. The
need for close control of surface irregularities may be relaxed
because the conductive ink may fill small voids or surface
imperfections. The fill performance may be adjusted by the
formulation of the ink.
[0023] Ink may spread over the substrate out of the boundary of the
set line width. Depending on the conductive ink used, ultraviolet
(UV) light or high power light source, including but not limited to
a laser, may be used to partially or totally sinter the ink when
being printed. Such that ink which is sensitive to UV light, the UV
light dries ink so that it does not expand. Metal lines confinement
within specified width is thus obtained. Other light sources, an
oven, or other means to promote desired melting and/or sintering of
the conductive ink deposited may also be used as specified by the
conductive ink manufacturer.
[0024] As stated earlier, one or more conductive layers may be
printed by the system of the present invention onto the array in
traces and as connection or contact points for electrical signals
to/from individual array elements via such traces. One or more
layers may also be directly printed over the one or more conductive
layers to act as passivation layers. Further, one or more auxiliary
layers (e.g., coatings) may be directly printed onto the array so
as to act as matching layers between the array and its environment.
An accurate acoustic match may improve the performance of the array
according to the application. Also, additional layers may be
directly printed, in whole or in part, onto the array to serve as
spacing layers.
[0025] Although the system is directed to depositing material onto
an array of electro-ceramic composite material, and in particular
1-3 electro-ceramic composite, the system may also be used for
depositing material onto any other substrate.
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] The foregoing objects, features and advantages of the
invention will become more apparent from a reading of the following
description in connection with the accompanying drawings, in
which:
[0027] FIG. 1A is a block diagram of the system of the present
invention;
[0028] FIG. 1B is a partial perspective view of part of the
rectangular 1-3 electro-ceramic composite array of FIG. 1A before
material is deposited by the system upon the array;
[0029] FIG. 2A is similar to FIG. 1B showing an example of material
deposited in diagonal traces, or generally parallel lines, along
the array by the system of FIG. 1A;
[0030] FIG. 2B is a top view of an example of a three by three
element array of FIG. 1A showing in more detail the connections to
array elements when material, such as conductive material,
deposited in diagonal traces or lines to make electrical
connections to elements along the array, for use of the array as
part of a finger print sensor and with additional material
deposited along individual array elements to assure proper contact
or connection thereto;
[0031] FIG. 2C is a top view of the array of FIG. 1A showing
schematically an example of material deposited along horizontal and
vertical traces or lines by the system of FIG. 1A for use of the
array as part of a finger print sensor;
[0032] FIG. 3A is a more detailed top view of two adjacent array
elements of the array of FIG. 2C by conductive material deposited
by the system of FIG. 1A to make a connection between array
elements;
[0033] FIG. 3B is a top view of six adjacent array elements of the
array of FIG. 2C illustrating undesirable wicking effect flow
causing unintended connection along the ceramic-polymer interface
between the elements by deposited material by the system of FIG. 1
when fluid viscosity of the deposited material is too low;
[0034] FIG. 4A is a top view of four adjacent array elements of the
array of FIG. 1A illustrating the deposit of a non-conductive
separator or barrier member in the case where the non-conductive
separator or barrier member when applied flow or wicks over
adjacent array elements;
[0035] FIG. 4B is a cross-sectional view along lines 4B-4B of FIG.
4A; and
[0036] FIGS. 5A, 5B, and 5C are perspective views the process of
fabricating an array electro-ceramic material using the system of
FIG. 1A, where FIG. 5A shows a substrate or plate onto which the
array of FIG. 1A is formed by dots or drops of electro-ceramic
composite material from the print head at desired array element
locations, FIG. 5B shows the dots or drops after being sintered and
filler material is provided, and FIG. 5C shows the array when
ground (or substantially leveled) to a target array thickness.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Referring to FIG. 1A, a block diagram of the system 10 of
the present invention is shown having a print head 13 of an ink-jet
type with a plurality of nozzles, such as numbering 16 or 128. The
print head 13 may be a part of a cartridge 16 providing a reservoir
with fluidic material for dispensing from the print head 13, as
typical of an ink-jet type print head. A separate reservoir or
container may also be used, rather than cartridge 16 to provide
fluidic material to print head 13. Print head 13 is movable by a
drive mechanism 12 in multiple dimensions, such as orthogonal
x,y,z, directions in which z is towards and way from the x,y plane
of a surface, plate, or substrate 18 supporting one or more arrays
20 of electro-ceramic composite material. Preferably, each array 20
is held or retained upon surface 18 by a fixture 19 having
rectangular openings each sized to receive one of arrays 20. For
purposes of illustration, three arrays 20 are shown, but one or
other number of arrays 20 may be provided.
[0038] An example of array 20 is shown in FIG. 1B of
electro-ceramic composite material comprising individual
piezoelectric elements 100 bound into a regular array by a filler
material 110, such as an epoxy or polymer (e.g., araldite and if
needed air filled vinyl micro-spheres). Array 20 can be made from
lead zirconate titanate (PZT) material having ceramic rectangular
(tower or pillar-like) elements in a matrix. The electro-ceramic
elements of array 20 can have shapes other than rectangular, such
as cylindrical or a partial tear drop shape (see FIGS. 5A-5C). The
ceramic elements 100 are relatively hard and brittle material
whereas the filler material 110 that fills the interstitial spaces
between the ceramic elements 100 may be considerably softer and
rather pliable. Such interstitial filler material 110 in addition
to binding the array together also suppress any shear waves so as
to increase acoustical attenuating and electrical isolation when
conductors are applied as described herein. For purposes of
illustration, the array of FIG. 1B is not shown to scale.
[0039] In a preferred embodiment, array 20 comprises rectangular
piezoelectric elements 100 that are 40 microns square by 100
microns deep, thereby yielding a dense array 20 having a 20 MHz
fundamental frequency sonic wave elements. A spacing of 10 microns
is used between elements is preferred in order to provide a
50-micron pitch between elements. Other geometries may be used,
such as for example, a pitch of greater than 50 microns.
[0040] Array 20 may be manufactured in the same manner as described
in the above incorporated patent before placement of conductors,
such as by laser cutting, dicing, molding, or screen-printing.
Laser cutting involves using an excimer laser to cut small groves
and thereby form the elements of array 20. Dicing involves using
high performance dicing equipment to form groves and the elements
of array 20. Molding involves using injection molding equipment to
form array 20, such as from a ceramic slurry. Screen-printing is a
technique similar to that of solder printing in the assembly of
printed circuit boards, where highly automated screen printing
machines are adapted with laser cut stencils. The fabrication of
array 20 may be the same as described in the above incorporated
U.S. patent, except where the part of the fabrication process
involving placement of conductive elements along the array 20, or
other layer(s) as described herein, is provided by system 10. Array
elements 100 may be shaped as shown by array 20a of FIG. 5C which
is fabricated by system 10 as later described below, which may also
be operated upon by system 10 in the same manner as described
herein in connection with array 20.
[0041] The drive mechanism 12 may be an x, y, z stage having a
motor enabling bidirectional motion in each of the x, y, z
dimensions (or axes). Alternatively, an x,y stage may be coupled to
surface 18 for movement in at x, y dimensions instead of or in
addition to mechanism 12.
[0042] A computer (computer system or controller) 11 has memory
having a program or software for controlling operations the system
10. Computer system 11 sends signals to the drive mechanism 12 to
move the print head 13 to desired locations and sends signals to
enable actuation of the print head 13 to control dispensing of
material provided from cartridge or reservoir via print head 13
onto array 20 when the drive mechanism is positioned in at x, y
coordinates at such locations at a desired distance in z spaced
there from. The memory of the computer system has a preset movement
and dispensing sequence (or program) which the computer system 11
follows to provide material from print head 13 nozzle(s) onto the
array 20 in the desired locations and amounts, such as to provide
dot(s), or trace(s) or line(s), as desired. Different passes over
the array 20 can be provided at the same or different locations for
depositing layers of the same material or different material from
print head 13.
[0043] The drop size for the print head 13 can be varied from 5 to
50 micron under control of the computer system 11, such as by
selecting a subset of nozzles and/or actuation time of the print
head 13. Step size by mechanism 12 in x and y dimensions may be in
5 microns or more, while in z dimension the print head can be moved
in millimeter steps, such as to preferably 700 microns above the
array 20. Thus, controlled dot(s), or trace(s) or line(s), of
material from print head 13 can be provided by system 10 to enable
material from print head 13 to be deposited upon one or more arrays
20 of FIG. 1.
[0044] The material which may be dispensed by print head 13 may be
conductive fluids, such as conductive metallic ink, or a
non-conductive fluid, such as a liquid polymer material. For
example, conductive metallic ink may be conductive nanoparticles
(e.g., silver) mixed together with a solvent so as to enable flow
via ink jet nozzles of print head 13 when actuated by computer
system 11. For example, the conductive metallic ink may be CCI-300
manufactured by Cabot Corp, but other conductive metallic inks may
be used. Also other conductive or non-conductive materials may also
be dispensed in other forms of a powder, a slurry, or a colloid
having proper viscosity for dispensing via nozzles of print head 13
when actuated by computer system 11. To change the material
dispensed in system 10 a different print head cartridge may be
provided, or the same print head cartridge re-filled with a
different desired material. Although a single print head 13 is
shown, multiple print heads may be provided which move in tandem by
the drive mechanism 12, or each separately attached to the drive
mechanism 12 when needed to deposit its respective material there
from under control of computer system 11.
[0045] One area that has seen enormous strides has been the
development of very high quality printing machinery. The recent
ability of equipment to deposit inks, fluids and colloids with high
accuracy and repeatability to a recipient material such as a
substrate material has meant that it is now possible to directly
deposit materials as a positive process. For example, system 10 may
utilize a high precision ink-jet printer 14, such as Fujifilm
Dimatix ink-jet printer, model no. DMP5000. Such printer 14
provides print head positioning (in x,y or x,y,z) and actuation
(i.e., printer 14 represents at least drive mechanism 12 and print
head 13 coupled thereto), and hardware/software interface to
computer system 11 enabling an operator to program the system 10 to
apply material(s) from print head 13 at desired locations over
surface 18. Other high-precision ink-jet printers may also be
used.
[0046] In operation, the system 10 enables a conductive material
via print head 13 to be deposited that is sufficiently tolerant of
vertical features of the 1-3 composite material of array 20. This
may sacrifice line edge definition such as may be provided by thin
film deposition based upon photolithographic process in return for
more robust step coverage and a reduction in the cleanliness
requirements that are implicit in the photolithographic process.
Further, simplification of the complexity associated with a vacuum
deposition may be beneficial.
[0047] Referring to FIGS. 2A, 2B, 2C, and 3A, system 10 provides
diagonal deposition of conductive ink 200 in traces as shown by
parallel lines in FIGS. 2A and 2B, or orthogonal grid of different
traces of conductive material along array 20, as shown in FIGS. 2C
and 3A. FIG. 2B further shows the same conductive ink 210 being
deposited by system 10 in one or more drops or droplets 210 from
print head 13 to provide contact points. Preferably, all traces are
made first at desired array locations along array elements 100 and
filler material 110 there between of desired line width, such as 30
microns wide, in order to deposit a first layer or conductive
material. Thereafter, at each location where a contact point or
connection to array element 100 is needed, one or more drops 210
are deposited in order to deposit a second layer of conductive
material. Preferably, such drop(s) are located upon each array
element 100 where a contact point is desired so as to provide an
oval shape of conductive material with such part of a trace of the
first layer already present on that array element. Deposition of a
layer may also be repeated, if needed. Depending on the viscosity
and chemical composition of the ink 200 and print head 13
dispensing thereof a desired size (width) traces and contact points
are provided. Good repeatability exhibited by high quality
precision machinery, such as Fujifilm Dimatix ink-jet printer
described above, provides repeated application can be used to
buildup thickness in material layers in a very selective way as
described herein.
[0048] In this manner, conductors being deposited in the first
layer can be selectively thickened at array 20 locations
corresponding to contact points on array elements 100 by the second
layer. The deposited conductive material 100 results in conductors
or conductive element interconnected in a grid (or lattice) as
desired upon array 20, as shown for example in FIGS. 2B and 3C.
After the first and second layers are deposited, one or more
additional layers may be selective deposited by system 10, such as
of photoresist material to provide passivation layer(s). Also
coating material may be applied by system 10 in one or more
layer(s), desired. The interconnected conductive elements may be
assembled with other parts and further connected using similar
direct deposition by system 10 of desired material(s).
[0049] Additionally, after depositing of the first and second
layers of conductive ink 200, such layers are sintered to remove
the solvent contained in the applied conductive ink. The type of
sintering depends on the particular conductive ink used. For
example, in the case of Cabot conductive ink mentioned earlier, the
entire array 20 is placed in a convection oven, such as for 30
minutes to 1 hour, until the ink is sintered as specified by the
manufacturer. In another less preferred example, the conductive ink
may 200 be manufactured by Inktec Co., Ltd. of South Korea.
Sintering with Inktec ink is by application of Ultraviolet (UV)
light from a light source 17 (FIG. 1A), or other high power light
source, during the print head 13 depositing of such conductive
material, as specified by the manufacturer. Such sintering may be
partial or total sintering as desired. Computer system 11 may
optionally control the operation of light source 17. Other light
sources, oven, or other means that increases temperature sufficient
to promote desired melting and/or sintering of the conductive
material may also be used as specified by the conductive ink
manufacturer. It is believed that sintering by light source 17
during the deposition process may control the spread of the fluidic
conductive material along the array 20 out of the predefined line
boundary locations where deposition is desired, and thereby assist
in confining conductors to a particular line width or dot size
applied. If a light source is not needed for sintering (or curing)
the particular ink, then light source 17 may be removed from system
10.
[0050] The deposited conductive material thus becomes a conductors
or conductive elements enabling desired electrical contacts to
array element 100 of the desired line width each to provide a
sensing element as described in the above incorporated patent. As
stated earlier multiple depositions by system 10 may be repeated at
the same array locations (or paths, lines, or traces) in order to
build-up layers of conductive material for passing electrical
signals. Although the above layers are discussed with respect to
the top of the array 20, after desired layers are provided by
system 10 along the top of array 20 the entire array is flipped in
fixture 19 so that bottom of the array 20 can be operated upon by
system 10 to deposit the layers of material at the same locations
as along the top of the array to make identical conductors (or
deposit other layer(s) described herein) when the array is to be
part of a fingerprint sensor as described in the incorporated
patent.
[0051] In the case of a 1-3 electro-ceramic composite, the surface
steps (or variations in surface flatness) between the two
constituent materials filter material 110 and electro-ceramic
material of array elements 100 may provide a channel where the
surface tension of the ink, fluid or colloid when deposited by
system 10 can causes diffusion in interstitial regions between
adjacent array elements 100. In certain circumstances, as
illustrated in FIG. 3B, and in FIG. 2 (bleeding 220 of conductive
ink 200), such as close spacing of the array elements 100 and with
very low viscosity of the fluid, the "wicking" effect may cause
short circuits between adjacent conductors that may be impractical
or impossible to correct. Regardless of surface cleanliness, the
surface tension effect may be pronounced. The viscosity of the
fluid deposited may be limited to a narrow working range because of
the limitations of the active constraints of the deposition
mechanism provided by print head 13.
[0052] Referring to FIGS. 4A and 4B, this problem may be overcome
by application of separator or barrier member of insulator,
non-conductive material 400 which is deposited by the system 10,
via print head 13 with cartridge 16 having such non-conductive
material, along the interstitial region(s) 114 between array
elements 100 where no connection by a conductive element is
desired. Preferably, non-conductive material 400 is a polymer
material, and thus deposition thereof is referred to herein as of a
polymer layer. Such polymer material may, for example be
photoresist, dispensed by the print head 13. Once upon the array
20, the polymer material at least partially solidifies (by
polymerization) to provide such polymer layer representing
insulating barriers avoiding undesired connections between the
particular array elements 100 separated by barriers when the
conductive material 200 are later applied by system 10 at or near
such array elements. Light source 17 may optionally be used during
depositing of the non-conductive material by system 10. There may
be a flow, bleeding or wicking of non-conductive material 400 as
shown in FIGS. 4A and 4B partially over the top surface 112 of
array elements 100. As such, the flow does not effect desired
electrical connectivity to the array element 100 by conductor
element 200, as best illustrated in FIG. 4B. Non-conductive
material 400 may be deposited repeated at the same location if
needed to build-up layers.
[0053] After the non-conductive polymer material is applied at
locations to provide the desired non-conductive barriers, the two
layers of conductive material 200 as described above are then
deposited by system 10 at desired locations and amounts in one or
more passes over array 20. The polymer layer preferably is then
removed, such in a manner common to the semiconductor industry.
However, removal of the polymer layer may be optional if such does
not effect conductors or subsequent layers. With the conductor
material 200 applied accurately by system 10 to adhere to the
electro-ceramic of array 20, the non-conductive material 400
barriers enables conductor material when deposited by print head 13
to easily flow (or bleed) where needed to provided desired
connections without the seeping effect seen at the interfaces of
the example of FIG. 3B. The bleeding, if any, over array elements
100 may be different than shown in FIG. 4B by control of the line
width or drop(s) of the non-conductive polymer material 400
deposited by system 10.
[0054] Because a composite material may show variation in size and
relative placement of the array elements 100, especially array
elements of electro-ceramic 1-3 composite material, the placement
of the traces along the array 20 and connection points upon array
elements 10 may vary. Accordingly, system 10 may use an optical aid
for alignment prior to application of material by print head 13.
Such alignment enables offset placement of print head 13 so that
conductive material or non-conductive material when deposited is
aligned so that each array element is connected desired regardless
of the offset from its intended position of array elements 10. In
the case where variation is linear across the dimensions of the
surface, then the programmed placement may be linearly scaled; for
example if the entire substrate is 5% larger or smaller due to
process uncertainties in the early part of fabrication, then the
programmed placement may be increased by the same linear 5%.
However where local distortion has occurred, an optical alignment
aid may be automated so as to scale individual connection points
though at the cost of operating speed. This feature of system 10
permits far greater process variation that is possible using a
photolithographic process where the photo mask is invariant and
dimension of array elements 100, which often vary from expected
position or size.
[0055] Preferably, the optical alignment aid is provided by pattern
recognition software programmed in system 10 to apply material from
print head 13 at positions where array structures 100 are present
in array 20. A camera 15 may be mounted adjacent the print head, or
in know offset spatial relationship thereto, to capture image(s)
focused on the array 20 or parts thereof (see dotted line). When
system 10 is programmed using computer system 11, the operator
utilizing a user interface on computer system 11 (e.g., graphical
user interface upon a display with keyboard, mouse or the like)
provides the objects (size and/or boundaries) of each of the array
elements in array 20, and the locations for each layer for material
deposition by system 10, which is stored in memory of the computer
system. As typical of pattern recognition software, camera 15
provides image(s) which are digitally processed to detect
boundaries of objects, match array elements 100 as objects to their
expected locations stored in memory, and adjusts print head
location (offset) accordingly so placement of material is accurate.
For example, such pattern recognition software and user interface
software enabling programming of the operation of the high
precision ink-jet printer 14 described above may be provided by the
printer manufacturer.
[0056] System 10 may be used in addition to apply conductive
material 200 or non-conductive barrier material 400 described above
may be used to fabricate array 20, rather than by a fabrication
methods described in the incorporated patent. In this case, the
material dispensed by print head 13 is an electro-ceramic material
deposited at locations to provide the desired array element size,
spacing between array elements, and total array size, of the
desired height. To produce the electro-ceramic material to be
deposited, electro ceramic material (PZT) may be crushed or
pulverized, and then following a drying process, the fine powder
resulting may be combined with a binder (e.g., an epoxy) and the
resulting fluid provided in the reservoir of a cartridge 16
installed in print head 13. The process to arrive at the fine
powder of PZT material may be considered calcining. For example,
FIGS. 5A, 5B, and 5C show the fabrication steps.
[0057] FIG. 5A shows a substrate or plate 18 onto which dot or
drop(s) 105 from the print head of FIG. 1A of electro-ceramic
composite material is deposited at array element locations. The
dots are thus at locations where each tower-like element of the
array is to be built. The thickness of the dots may each be a
single dispensed drop or built up by repeated overprinting of
multiple dots to greater than a target thickness (height upon
substrate 18). The target thickness may be 100 microns. Once at
least the target thickness (and size) of the dots 105 has been
achieved, then sintering is performed, such as by dot by dot basis
using a laser.
[0058] The sintering process preferably comprises a "flash"
sintering whereby the targeted volume is brought very rapidly to
sintering temperature and also cools rapidly. Where the
electro-ceramic material so deposited contains lead as a
significant component, one of the significant process concerns is
the ablation of the lead during the soak at sintering temperature.
This can be a lengthy process which may deplete the lead content
severely and thus sacrifice many of the desirable properties of the
electro-ceramic material. By controlling the time spent at
sintering temperatures to the minimum needed, lead depletion may be
substantially mitigated. Because the sintering no longer occurs in
the bulk, warping and distortion may be reduced.
[0059] After sintering, filler material 110 (e.g., epoxy) is added
over the dots 105 and regions there between to provide a
rectangular block 111 as shown in FIG. 5B. Once filler material 110
polymerizes, grinding along the top of block 111 then is performed
to reduce the thickness of the block and provided finished array
20a with the target height and a sufficiently flat surface 115, as
shown in FIG. 5C, so that the top of each array element of the
desired size is present along surface 115. It is desired that the
top array surface of array 20a (or array 20) has as little
variability, but system 10 can accurately apply material(s) along
an array surface even with thickness or dimensional variation which
is on average 400 nm. Deposit of materials by system 10 thus has
more tolerance to variability of the surface flatness than
photolithographic depositing of conductive material, and thus
system 10 deposition does not have the disadvantages described
earlier of less preferred photolithographic metal deposition.
[0060] With the array 20a fabricated by system 10, system 10 may
then be utilized to deposit the first and second conductive layers
as described earlier on the fabricated array 20a in the same manner
as array 20 to make traces and connection points, and if desired a
polymer layer prior to depositing such conductive layers.
[0061] The substrate 18 with drops 105 formed thereupon is
preferably removed from placement below print head 13 for carrying
out the sintering process, such as by mounting the substrate 18 to
a laser mounted stage positional over each dot 105 (or group of
dots) for the desired duration and cross-sectional spot size. After
addition of filler material 100, the resulting block 111 is
presented to a grinding machine to provide array 20a of FIG. 5C.
The array may then be placed back upon surface 18 in fixture 19
under the print head 13 of system 10 for depositing conductive
material 200 (with or without non-conductive barriers) as described
earlier.
[0062] The deposition of material as a printing process by system
10 as illustrated for example in FIGS. 5A-5C facilitates the
production of uniquely shaped piezoelectric elements and
combination of elements of the same or different geometric shapes
or size.
[0063] From the foregoing description it will be apparent that
there has been provided an improved system and method for system
and method for the depositing material (conductive or
non-conductive) on a piezoelectric array and for fabricating such
array. The illustrated description as a whole is to be taken as
illustrative and not as limiting of the scope of the invention.
Such variations, modifications and extensions, which are within the
scope of the invention, will undoubtedly become apparent to those
skilled in the art.
* * * * *